From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752357AbeCNVBB (ORCPT ); Wed, 14 Mar 2018 17:01:01 -0400 Received: from mail-qt0-f196.google.com ([209.85.216.196]:45931 "EHLO mail-qt0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752003AbeCNVA4 (ORCPT ); Wed, 14 Mar 2018 17:00:56 -0400 X-Google-Smtp-Source: AG47ELvqa5JEHFzQbPGUK0Ng1kW6BFIg0pnTQBjL9W+n4zzQUNs4AlX5LozhkfsCyfT6b8qpX3F1Tw== From: Ram Pai To: mingo@redhat.com Cc: mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, x86@kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, dave.hansen@intel.com, benh@kernel.crashing.org, paulus@samba.org, khandual@linux.vnet.ibm.com, aneesh.kumar@linux.vnet.ibm.com, bsingharora@gmail.com, hbabu@us.ibm.com, mhocko@kernel.org, bauerman@linux.vnet.ibm.com, ebiederm@xmission.com, linuxram@us.ibm.com, corbet@lwn.net, arnd@arndb.de, fweimer@redhat.com, msuchanek@suse.com, Ulrich.Weigand@de.ibm.com Subject: [PATCH v3] x86: treat pkey-0 special Date: Wed, 14 Mar 2018 14:00:14 -0700 Message-Id: <1521061214-22385-1-git-send-email-linuxram@us.ibm.com> X-Mailer: git-send-email 1.7.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Applications need the ability to associate an address-range with some key and latter revert to its initial default key. Pkey-0 comes close to providing this function but falls short, because the current implementation disallows applications to explicitly associate pkey-0 to the address range. This patch clarifies the semantics of pkey-0 and provides the corresponding implementation on powerpc. Pkey-0 is special with the following semantics. (a) it is implicitly allocated and can never be freed. It always exists. (b) it is the default key assigned to any address-range. (c) it can be explicitly associated with any address-range. Tested on x86_64. History: v3 : added clarification of the semantics of pkey0. -- suggested by Dave Hansen v2 : split the patch into two, one for x86 and one for powerpc -- suggested by Michael Ellermen cc: Dave Hansen cc: Michael Ellermen cc: Ingo Molnar Signed-off-by: Ram Pai --- arch/x86/include/asm/pkeys.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/pkeys.h b/arch/x86/include/asm/pkeys.h index a0ba1ff..6ea7486 100644 --- a/arch/x86/include/asm/pkeys.h +++ b/arch/x86/include/asm/pkeys.h @@ -52,7 +52,7 @@ bool mm_pkey_is_allocated(struct mm_struct *mm, int pkey) * from pkey_alloc(). pkey 0 is special, and never * returned from pkey_alloc(). */ - if (pkey <= 0) + if (pkey < 0) return false; if (pkey >= arch_max_pkey()) return false; @@ -92,7 +92,8 @@ int mm_pkey_alloc(struct mm_struct *mm) static inline int mm_pkey_free(struct mm_struct *mm, int pkey) { - if (!mm_pkey_is_allocated(mm, pkey)) + /* pkey 0 is special and can never be freed */ + if (!pkey || !mm_pkey_is_allocated(mm, pkey)) return -EINVAL; mm_set_pkey_free(mm, pkey); -- 1.8.3.1